The objectives of the Branch Vein Occlusion Study are to document the natural history and determine if photocoagulation treatment is useful in the management of branch vein occlusion and its complications. The treatment by argon laser photocoagulation will be evaluated for the management of 1) major branch vein occlusion without neovascularization; 2) major branch vein occlusion with neovascularization; and 3) branch vein occlusion with macular edema and decreased vision. We will attempt to determine if argon laser photocoagulation is more effective than the natural course in each of these three categories by carefully monitoring patients for visual acuity changes, neovascularization, vitreous hemorrhage and/or macular edema. The method of accomplishing the above is to recruit a total of 62 patients from each of 5 centers. Each patient will be randomized into either a treatment (argon laser photocoagulation) or control group. Recruitment of patients takes place during the first 2 years of a 5 year study. The remaining 3 years will be spent following and carefully recording changes in each patient.